Is a new electrical service for the garage an option for you? The reason I asked is because I had a similar situation and after much careful thought I decided to go with an independent electrical service for the garage.
When the wife and I bought our house we had two number 14 gauge wires running to the one car detached garage. I have a whole bunch of power tools, some of which draw a fair amount of power to run. I buried in conduit a number 8 gauge wire and ran it from the breaker panel in the house out to a breaker panel in the garage. This worked out fairly well, I could now work out in the garage without any real big problems, but I had a very limited amount of power I could use. I should mention here that in the house we only have a 100 amp service. This meant that between the house and the garage we could only use 100 amps before the main breaker would trip. So in the Summer when it was hot and we are running the central air, the wife was cooking on the electric stove while baking a pie in the oven, the dehumidifier was running in the basement and she had a load of wash drying in the dryer, that didn't leave a great deal of power for me to use in the garage.
So when we built the new detached garage I decided it would be best to have a separate 200 amp service and that way I could use whatever amount of power I wanted and it would not have any effect on the amount of power being used in the house. I realize there is an additional cost involved in doing this, around here the meter charge is a little less than $9 per month. But the electrical company ran the power lines from the street to the house and connected them to the meter for free. So now I have all the electrical power in the garage I need to run my equipment and it does not interfere with anything that is going on in the house, although I do have the extra meter charge to pay every month. But it is a small price to pay for having all the power I need to do the things I want to do in the garage/workshop.
This may not be something that would work for everyone, but for me it worked out extremely well. I just thought I would mention it, perhaps it would work pretty good for you too. In any case, it is an option for you to consider, especially if you have some equipment that takes a lot of power to operate.